I'm writing a fantasy-medieval story in which one of the main characters has extensive knowledge of human anatomy. He knows all of the organs and what they do, and knows things like where muscle groups are located and where nerves are. Basically if it could be found out in medieval times, he knows it.
I want him to be able to use this knowledge to control exactly how much pain his victims feel. The problem is that I do not have much knowledge at all of human anatomy, and am not sure how far this character's knowledge could take him.
I want him to be able to kill someone quickly and painlessly. I also want the opposite: for him to be able to kill someone as slowly and painfully as possible. He should also be able to cause a lot of pain without actually killing the victim.
I don't know how he would do these things, or if they are even possible (thinking specifically of the painless one). So I have two questions disguised as one: using only swords, daggers, or similar weapons, can an individual both kill someone quickly and painlessly as well as slowly and painfully, as well as causing maximum pain while not killing the victim? If this is possible with medieval weaponry, how would it be accomplished? What areas of the anatomy would he target?
I apologize for the rather grisly topic. He's a rather grisly character. I tried doing a Google search to answer this question, but only got things like suicide hotlines.